China's air force is gearing up for its biggest ever assault on the clouds to ensure blue skies above Beijing for the 60th anniversary of communist party rule, local media reported today.

Eighteen cloud-seeding aircraft and 48 fog-dispersal vehicles are on stand-by to intercept rainclouds that threaten to cast a shadow over the festivities, which will include the biggest display of military power in at least 10 years.

"It is the first time in Chinese history that artificial weather modification on such a large scale has been attempted," said Cui Lianqing, an air force meteorologist, speaking to the Global Times newspaper.

Meteorologists will coordinate the mission using satellite data. The Beijing Weather Modification Office will supplement the air force's campaign with rockets and planes that load the clouds with silver iodide or liquid nitrogen — dry ice — to induce precipitation above reservoirs and rivers.

China has the world's most extensive rain creation infrastructure, employing about 50,000 people nationwide. Their job is usually to alleviate droughts in the arid north of the country. For national day they would have to encourage rain to fall from clouds before they reached Beijing.

The National Day events mark the founding of the People's Republic of China on 1 October, 1949. The communist party wants to use the occasion to showcase its achievements since Mao Zedong took power.

The centre of the city will be closed off for a huge parade, musical performance and show of military power. Clear skies are needed for the

firework display and fly past by air force jets.

Smog is another concern. Although air pollution has eased since the Olympics, when more than 100 factories were relocated and restrictions were imposed on cars, the Beijing authorities are taking no chances.

Environment officials have said they will inspect construction sites, regulate coal-burning facilities and impose extra restrictions on vehicles with high levels of exhaust fumes.

Inner Mongolia, Henan, Hebei and other neighbouring regions that host large-scale industrial parks have agreed to cooperate in reducing emissions ahead of the anniversary.

Fearing a major pollution incident might dampen the festive mood, the Ministry of Environmental Protection has mounted a week-long inspection of areas where accidents often happen or where dangerous chemicals are produced. Water supplies are being checked more stringently than usual.

Some of the security measures have frustrated many Beijingers. During rehearsals in recent weeks, residents along the route of the parade were instructed not to go on to their balconies or take pictures of tanks and other vehicles.

The authorities have banned the sale of knives in supermarkets and declared a no-fly zone for kites and racing pigeons. Whether non-compliant birds will suffer the same fate as wandering clouds has not been revealed.

Ten years after taking power, Mao Zedong declared a war on nature, including a disastrous campaign to eradicate sparrows, and a commitment to induce rain. "Manmade rain is very important. I hope the meteorological experts do their utmost to make it work," he said.

Today, however, the military admits there is a limit to their ability to control nature. "There are still a lot of uncertainties with the

weather," Cui told the Global Times. Past records suggest there is a 30% chance of rain on October 1, it said.